Gaetan it’s a 3M product, the sandpaper is so fine it’s more of a polishing action than anything, http://catalogue.3m.eu/en_EU/EU-AERO/Abrasives/Wet_Sanding/Perfect_it-III~Microfine_Abrasive_Paper~314
I found the plastic that gets dragged onto the camera contact pins by the sliding spring loaded flash pins to be very persistent and hard to get rid of so I had to resort to the microfine paper. If you have a plastic knife handy/available just wrap a small piece around the back edge of that to carefully clean the camera contacts without contacting the rest of the shoe area (as much as possible).
My earlier two cameras don’t suffer from this problem only the A700 does, its shoe seems to be of a softer plastic compound than the KM5D and the A100, the shoe area in those seems to be a separate part and made of different harder plastic.
I suppose it’s the human condition, we progress but at the same time forget how to do things we already learnt before, thus we are condemned to repeat/recycle mistakes over and over.
Then of course there is the economic perspective also, I suppose some bean counter wiz-kid got a bonus for saving the company the expense of having to separately make the part out of more expensive plastic with the attendant extra difficulty with the pins, the soft plastic would probably allow the pins to be heated and pressed into position and become ‘welded’ to the plastic, whereas the hard plastic assembly would most likely have to be cast/moulded with the pins held in their proper position, conforming to tolerances, and most likely be a more expensive part.